I just purchased a Proto 2000 Frisco E8 from a gentleman here in Union who converted from HO to O scale. I got it for an amazing $20.00. It looks mint and runs great, except I noticed that the rear wheels on the front truck bob up and down as it moves down the track, causing it to derail in some spots, especially on a curve where I have a "paved" crossing. The motion is similar to car traveling down the interstate with a tire out of balance. If anyone can shed some light on why the wheels are doing this and how it can be corrected, it would be greatly appreciated. Pat Moreland, Union Mo.